BoxFit

15" x 9-1/2" inside · $12.51 online · up to 70 lb

Priority Mail Legal Flat Rate Envelope

Same idea as the regular envelope but 2.5 inches longer — built for legal-size paper, it also takes longer flat items. Enter your item below to check the fit and compare it with every other option.

Popular items

Item size (L × W × H)

in
in
in

Weight

lb
oz
in
Packed size
6.75 × 5.25 × 0.5 in
Actual weight
4 oz
Dim weight
n/a (≤1 ft³)

Dimensional weight = L × W × H ÷ 166, used by USPS only above 1 cubic foot (18 in³ now). Prices: USPS Notice 123, effective October 4, 2026.

Cheapest way to ship

USPS Ground Advantage

$8.24

Zone 5, billed at 4 oz · 2–5 days. Next best: Flat Rate Envelope at $11.97 — you save $3.73.

Legal Flat Rate Envelope

FITS - $12.51

Drag to turn · box outline = inside size

  • Ground Advantage (your own box)BEST PRICEZone 5 · billed 4 oz$8.24

Tap a box to see it in 3D. Flat Rate prices are the same in every zone.

The Priority Mail Legal Flat Rate Envelope measures 15" x 9-1/2". In centimeters that is about 38.1 × 24.1 cm. Because an envelope wraps around what's inside, a thicker item uses up length and width: an item 1 in. thick can be at most about 14.0 × 8.5 in.

Where you buy postagePrice
Online label (USPS.com, shipping apps)$12.51
Post Office counter$14.25

The price is the same to every address in the 50 states, whether it weighs 2 ounces or 70 pounds. Buying the label online saves $1.74 per package. These are the prices in USPS Notice 123, effective October 4, 2026; USPS updates them each January and July, and the packaging itself is free.

Here is what a parcel of the same size would cost by USPS Ground Advantage (online label) at different weights and distances. Green cells are where the Legal Flat Rate Envelope at $12.51 is cheaper.

WeightGround, zone 2Ground, zone 5Ground, zone 8
8 oz$7.34$8.24$8.95
1 lb$8.08$9.29$11.22
2 lb$8.48$10.50$13.42
5 lb$10.41$14.53$20.24
10 lb$12.91$17.81$26.39
20 lb$18.11$26.68$42.14

Going cross-country (zone 8), the Legal Flat Rate Envelope beats Ground Advantage from about 2 lb. For a nearby address (zone 2) it takes about 10 lb before flat rate wins. The calculator above does this comparison for your exact item and zone.

Typical things people send in it: legal-size contracts, a pair of leggings, long flat prints, a thin hardcover.

From our presets, these fit: video game (6.75 × 5.25 × 0.5 in).

Too big for it: shoebox (no flat rate option — use Ground Advantage); hoodie (fits the Medium Box (Side-Loading)); 3 books (fits the Medium Box (Top-Loading)); laptop (fits the Medium Box (Side-Loading)); phone (fits the Padded Flat Rate Envelope).

The item must fit with the flap closing normally — USPS does not allow taping a flat rate envelope wider or taller to squeeze more in.

Both are 9-1/2 in. wide, but the Legal envelope is 15 in. long instead of 12-1/2 in. It costs $0.54 more online ($12.51 vs $11.97). Use it when a document or flat item is longer than about 11 inches; otherwise the regular envelope is the cheaper Priority Mail option.

Frequently asked questions

How much is a legal flat rate envelope in 2026?

$12.51 with an online label and $14.25 at the Post Office counter (USPS Notice 123, effective October 4, 2026).

Is there a weight limit for the legal flat rate envelope?

Yes, 70 lb — the same limit as all Priority Mail. Up to that, weight doesn't change the price.

Where can I get a legal flat rate envelope?

Free at any Post Office or ordered free from the USPS online store. You must use the official USPS Flat Rate packaging to get the flat price.

How long does a legal flat rate envelope take to arrive?

It ships as Priority Mail, which USPS schedules for 1–3 business days. Delivery times aren't guaranteed.